The present invention concerns stabilization of polyoxyalkylene polyether polyols and the use of the stabilized polyols in the preparation of polyurethane foam. In particular the invention relates to stabilization of polyols with certain liquid stabilizer compositions and the color or scorch inhibition of flexible and semiflexible polyurethane foams made from the stabilized polyols.
Prior art methods for stabilization of polyoxyalkylene polyether polyols with solid antioxidants or stabilizers and the use of the stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known.
Conventional solid stabilizers are generally dissolved in the polyol media by heating. To remove any undissolved stabilizer solids, the entire voluminous polyol mass is subjected to a filtration step. Then the polyol precursor can be processed into the final foam product.
U.S. Pat. No. 4,933,374 discloses a liquid stabilizer composition composed of 2,6-di-tert-butyl-4-sec-butylphenol and a reaction product of diisobutylene, styrene and diphenylamine. The liquid stabilizer eliminates certain processing disadvantages associated with solid stabilizer systems. The liquid stabilizer compositions are readily soluble in the polyol media at ambient temperatures. Consequently, two steps of the conventional process may be eliminated: dissolution of the stabilizer in the polyol media by heating and removal of undissolved stabilizer solids by filtration. Furthermore, the liquid stabilizer compositions may be added to the polyol by metering or pumping for convenience and safety.
Another known scorch inhibitor is phenothiazine disclosed in U.S. Pat. No. 3,214,397. U.S. Pat. No. 4,010,211 teaches the replacement of part of a solid stabilizer system composed of butylated hydroxytoluene and p,p'-dialkyldiphenylamine with phenothiazine or its alkyl derivatives.
U.S. Pat. No. 4,275,173 discloses a solid synergistic stabilizer system consisting of a sterically hindered phenolic antioxidant, 4,4'-bis (.alpha.,.alpha.-dimethylbenzyl)diphenylamine and phenothiazine or its alkyl derivatives.
Surprisingly, it has been discovered that phenothiazine and certain alkyl derivatives of phenothiazine can be added to the liquid stabilizer composition composed of 2,6-di-tert-butyl-4-sec-butylphenol and a reaction product of diisobutylene, styrene and diphenylamine without destroying the liquid character of the stabilizer composition, while synergistically improving the overall scorch inhibiting properties of the stabilizer.